Questions and answers

Why urea gives a positive biuret test?

Why urea gives a positive biuret test?

Proteins are the complex compound formed by thousands of amino acids. Biuret is a compound formed by heating urea at 1800 which results in the condensation of 2 molecules of urea. The peptide bonds in Biuret give a positive result for the test hence the reagent is named so.

What is the confirmatory test of urea?

Biuret test is actually a confirmatory test for urea. For this you have to take a boiling tube. In this a little of the given substance is added & heated until it melts & then solidifies. Cool for a while & dissolve the residue in little water .

How is biuret formed from urea?

Biuret is typically produced from urea through a series of non-catalytic py- rolysis reactions at temperature above 130 oC (melting temperature of urea). At high tem- perature above the melting point of urea, one molecule of urea de- composes into equimolar amount of ammonia and cyanic acid.

What is biuret test used for?

Biuret test is used for detecting compounds with peptide bonds. A biuret reagent may be used to test the aqueous sample. This blue reagent is made by combining sodium hydroxide and copper sulfate solutions.

What Colour is biuret?

We used Biuret’s reagent to detect the presence of proteins in solution. The reagent is pale blue when pure, but when mixed with proteins, the resulting reaction produces a pale purple color.

Why is NaOH used in biuret test?

The reagent used in the Biuret Test is a solution of copper sulfate (CuSO4) and sodium hydroxide (NaOH). The NaOH is there to raise the pH of the solution to alkaline levels; the crucial component is the copper II ion (Cu2+) from the CuSO4.

What is the normal range of urea?

The normal range of urea nitrogen in blood or serum is 5 to 20 mg/dl, or 1.8 to 7.1 mmol urea per liter. The range is wide because of normal variations due to protein intake, endogenous protein catabolism, state of hydration, hepatic urea synthesis, and renal urea excretion.

What is difference between urea and urine?

Urea is the chief nitrogenous waste, which is eliminated through urine. Urea is produced in the liver from ammonia, which is a metabolite of amino acids and carbon dioxide. Urine is formed by the nephrons after filtration, secretion and reabsorption.

How do you reduce biuret in urea?

Biuret is selectively removed from urea by treating the urea in an aqueous solution at a pH above about 12.5 and a temperature between about 0.

What is a biuret in urea?

Biuret is an impurity in urea fertilizer caused by a side reaction at higher temperatures during processing. It has been identified as injurious to citrus foliage and to certain germinating seeds. The earliest urea plant designs produced urea with up to five percent biuret.

What is the principle of biuret test?

The biuret method is based on the fact that proteins (and, as a rule, all substances containing two or more peptidic bonds) react with copper to form a colored complex whose absorption (λmax= 454 nm), in the presence of excess copper, is proportional to the amount of protein present.

What is the result of the biuret test?

It is the result of the condensation of 2 molecules of urea. The peptide bonds in Biuret give a positive result for the test hence the reagent is named so. Biuret test is a general test for compounds (proteins and peptides) having two or more peptide (CO-NH) bonds. Histidine is the only amino acid that gives Biuret test positive.

Why is the copper reagent called the biuret test?

Despite its name, the reagent does not in fact contain biuret ((H2N-CO-)2NH). The test is named so because it also gives a positive reaction to the peptide-like bonds in the biuret molecule. In this assay, the copper(II) binds with nitrogens present in the peptides of proteins.

How is the biuret reaction used to assess protein concentration?

The biuret reaction can be used to assess the concentration of proteins because peptide bonds occur with the same frequency per amino acid in the peptide. The intensity of the color, and hence the absorption at 540 nm, is directly proportional to the protein concentration, according to the Beer–Lambert law .

What kind of alkali is used in biuret test?

*Presence of magnesium and ammonium ions interfere in biuret test. This can be overcome by using excess alkali.